The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by several turbojet engines each housed in a nacelle which also houses a set of auxiliary actuating devices associated with the operation thereof and performing various functions when the turbojet engine is operating or stopped. These auxiliary actuating devices comprise in particular a mechanical thrust reversal system.
A nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section housing thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is usually ended by an ejection nozzle, the outlet of which is located downstream of the turbojet engine.
Modern nacelles are intended to house a turbofan engine capable of generating, through rotating fan blades, hot air flow (also called primary flow) originating from the combustion chamber of the turbojet engine, and cold air flow (secondary flow) which flows outside the turbojet engine through an annular passage, also called flow path, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected from the turbojet engine through the rear of the nacelle.
The role of a thrust reverser, during landing of an aircraft, is to improve the braking ability thereof, by redirecting forward at least a portion of the thrust generated by the turbojet engine. In this phase, the thrust reverser obstructs the flow path of cold air flow and directs it towards the front of the nacelle, thereby generating a counterthrust which adds to the braking of the aircraft wheels.
Means implemented to achieve this cold flow redirection vary depending on the type of thrust reverser. However, in all cases, the structure of a thrust reverser comprises movable cowls displaceable between, on the one hand, a deployed position in which they open a passage in the nacelle for the diverted flow and, on the other hand, a retracted position in which they close this passage. These cowls can fulfill a function of deflection or simply activation of other diverting means.
In the case of a cascade-type thrust reverser, redirection of the air flow is performed by deflecting cascades, the cowl only having a mere sliding function intended to uncover or re-cover these cascades. Complementary blocking doors, also called flaps, activated by the sliding of the cowling, usually make it possible to close the flow path downstream of the cascades so as to allow redirection of cold flow towards the cascades.
These flaps are pivotally mounted on the sliding cowl between a retracted position in which they ensure, with said movable cowl, the aerodynamic continuity of the inner wall of the nacelle, and a deployed position in which, in a thrust reversal situation, they close at least partially the annular channel in order to divert a gas flow towards the deflecting cascades uncovered by the sliding of the movable cowl.
The pivoting of the flaps is guided by links attached, on the one hand, to the flap, and on the other hand, to a fixed point of the inner structure delimiting the annular channel.
Such a configuration of the prior art has several problems, namely, in particular, problems of differing opening kinematics between the translational movement of the cowling and the pivoting of the flaps, problems of aerodynamic disturbances due to the driving links passing through the flow path, problems of acoustic performances due to the installation of fixed articulation points which reduces the surface of the inner structure which can be used for an acoustic treatment, and mechanical problems due to the mechanical connection by the links between the thrust reverser and the inner structure.
The problem of the kinematics of the flaps opening degree with respect to the sliding of the cowl and, consequently, the problem of the management of the total cross-sectional area of air flow, is a particularly important issue.
Indeed, during a transition phase between opening and closure of the thrust reverser, the opening of the flaps, at the beginning of the opening phase of the mobile cowl, is faster than the rearward movement of said cowl.
There is often a kinematics sensitive point which places the flap in a position of partial obstruction of the annular channel without the obstructed section being completely compensated by the upstream section uncovered by the rearward movement of the mobile cowl.
The upstream section of passage through the thrust reverser cascades being lower than the section of the flow path which is obstructed by the flaps, this results in an increase of pressure in the engine, which makes it sensitive to manage the turbojet engine conditions in this transitional phase.
Several solutions have been implemented so as to solve one or more of these problems.
Thus, it is known to provide a thrust reverser architecture which no longer comprises a link passing through the annular channel.
For example, this objective can be achieved by providing for driving links articulated on the mobile flap and connected in the vicinity of the rear frame of the deflecting cascades. Such a solution is described in documents U.S. Pat. No. 5,228,641 and US 2007/0234707 for example.
Yet, such an architecture is unsuitable for turbojet engines with high bypass ratio.
Indeed, with this type of turbojet engine, the cascades length and, consequently, the movement of the cowl downstream of the nacelle to uncover the cascades, must be significant.
However, due to lack of available space in the nacelle, the length of the links cannot be sufficient to achieve opening kinematics adapted to the flaps and the cowl.
As a result, the flap is deployed very rapidly in the annular channel at the beginning of the rearward stroke of the sliding cowl, causing a significant increase in pressure in the annular channel.
It does not therefore solve the problem of appropriate management of the total cross-sectional area of air flow in the nacelle.
In addition, such a system raises problems of flow path sealing, as the sealing diaphragm has to be placed above the deflecting cascades. This implies, in particular, the transfer of the forces exerted on the flaps through fittings sliding between two cascades, which puts an additional burden on the structure and makes it more difficult to carry out.
Other devices which make it possible to adapt the kinematics of opening of the flap with respect to that of the rearward movement of the cowl are also known, in particular by setting some delay in the opening of the flap, thereby preventing an increase in pressure in the flow path.
However, the opposite disadvantage occurs, the upstream section of the air passage through the thrust reverser cascades, added to that of the two air flows in a direct jet mode being too significant compared to the air inlet section of the nacelle. Such a situation is also detrimental to the turbojet engine.
Furthermore, other devices providing an architecture lacking the link in the flow path provide for flaps sliding along suitable rails via rollers, along the movable cowl when its moves downstream of the nacelle.
However, these devices have deficiencies in terms of mechanical reliability, as they are subject to the wear of the movable parts, such as the rollers, the forces being applied point-wise on very small contact surfaces.
Therefore, there exists a need for improving thrust reverser devices lacking a link in the annular channel in order to overcome the aforementioned limitations. These solutions should, in particular, allow for an isostatic driving of the flaps, that is to say, a position of the movable cowl of the thrust reverser corresponds to a position of the flap, and use of conventional joints between the mechanical elements which do not require any point-wise contact or linear contact (as with rollers or balls) in order to limit the wear of the movable parts.
A first solution has been developed and described in French patent application FR 2 952 128 on behalf of the applicant.
The document FR 2 952 128 describes such a thrust reverser device equipped with at least one blocking flap pivotally mounted via one end on the movable cowl and associated with a driving system comprising at least one assembly forming a lever pivotally mounted on the cowl and articulated at each of the ends thereof, by means of driving links, respectively on the flap and on a fixed structure of the device.
Such a device makes it possible to eliminate the flap driving links placed into the flow path and the opening kinematics of the flap and the cowl is brought under control in order to ensure an almost constant air exhaust section in the nacelle, particularly when the thrust reverser device is in the configuration of a beginning of transit wherein the opening of the deflecting means by a translational movement of the movable cowl is low.